Isoleucine has a regulatory effect on glucose transport and metabolism in the body and has been suggested to have a hypoglycemic (blood sugar lowering) effect when taken before glucose/carbohydrates. While this has been observed in animals,[1] human clinical trials so far have shown inconsistent results, and the clinical relevance of this effect is questionable.[2][3][4]
Alternatively, in vitro and animal studies suggest that BCAAs can induce insulin resistance[5] and that BCAA-restricted diets (especially isoleucine-restricted ones) can improve insulin sensitivity and weight status.[6][7] While some human observational data reports that increased consumption of BCAAs is associated with increased body mass index (BMI),[6] other research has found the opposite effect.[8][9] The long-term effects (both potentially positive and negative) of a BCAA-restricted diet in humans have been largely unexplored, and the few small and short-term trials that have been done have found inconclusive effects.[10][11]